1. Field
The technology described herein relates to optical detection systems.
2. Related Art
Solid state image sensors, often referred to as “imagers,” detect incident radiation and produce, or provide, an image based on the detected radiation. A typical imager comprises a two-dimensional array of photodetectors (referred to as a focal plane array, or an imaging array) in combination with a readout integrated circuit (ROIC). The photodetectors are sensitive to (i.e., detect) incoming radiation and produce an output signal (referred to as a “photoresponse”) based on the detected radiation. The ROIC scans and quantitatively evaluates the outputs from the photodetectors, and processes them to create an image indicative of the radiation dispersion across the array of photodetectors. Because of their ability to produce images, imagers are useful in various applications, such as professional and consumer video, still image photography, remote surveillance, astronomy, and machine vision.
Conventionally, imagers have been used to detect radiation in the visible spectrum (i.e., radiation having a wavelength between 400-700 nanometers). Some conventional imagers, such as black and white imagers, merely detect the intensity of radiation in the visible spectrum, and provide little or no information about the specific wavelength of the detected radiation within the visible spectrum. However, conventional color imagers not only detect the intensity of radiation in the visible spectrum, but also provide information about the wavelength (indicative of color) of detected visible radiation.
Color imagers use different pixels within an imaging array to detect different colors within the visible spectrum, as shown in FIG. 1, which illustrates an exemplary arrangement of pixels 12 in an imaging array 10 of a conventional color imager. The imaging array 10 includes n rows and m columns of pixels. Each 2×2 pixel grouping has two green pixels 12G, one red pixel 12R, and one blue pixel 12B, commonly referred to as a Bayer pattern. Each pixel detects only radiation in a portion of the visible spectrum surrounding the designated color in the visible spectrum, and outputs a corresponding output signal. The raw output of the imaging array comprises a single color at each pixel. Before being displayed, each pixel typically is assigned a value for each of the three colors, red, green, and blue, e.g., by interpolation.
In conventional CMOS color imagers, each pixel includes a polymeric filter, usually on the top of the pixel. The wavelength of light detected by a given pixel is determined by its filter. For example, a green pixel, such as pixel 12G, has a filter made from a polymer that passes green light. Similarly, blue pixels have filters made from polymers that pass blue light, and red pixels have filters made from polymers that pass red light.